1. Field of the Invention
The present invention relates generally to the field of wind tunnel testing of aircraft designs. More specifically, the present invention is a method of and system for gathering off-body pressure signature data from a scaled model.
2. Description of the Related Art
As a consequence of the high public annoyance to the noise generated by sonic booms, Federal regulations currently prohibit supersonic overland flight by commercial aircraft. Sonic boom suppression of supersonic aircraft is desirable to decrease public annoyance, and, thereby allow unrestricted supersonic flight overland. To validate design, an efficient, accurate method of gathering off-body pressure signature data using a scaled model in a wind tunnel is needed.
The general process of performing wind tunnel tests to gather off-body pressure signatures of scaled models is known technology. The conventional method uses one or more single port static pressure probes. Various means of gathering the extent of the signature have been employed. These include fixing the model position in the tunnel and traversing the probe; fixing the probe position and traversing the model; or a combination of these two techniques such that the extent of the off-body pressure signature is measured. Either model or probe may be traversed mechanically or manually. Pressure measurements may be taken continuously while either model or probe is traversed at a constant rate or be taken in a traverse/pause mode. In the transverse/pause mode all movement is halted and the pressure field is allowed to become fully static before each pressure reading is recorded. After the data is collected, the model/probe relative position is changed by a fixed distance and data is once again gathered. This process is repeated until the entire distance of interest is covered.
The preferred method of off-body pressure signature measurement is to mechanically traverse the model with the probe in a fixed position; this process minimizes variability in the probe measured pressures. Repositioning the probe in the tunnel between measurements introduces errors to the reading. This is because the probe not only sees the pressure signature data gleaned from the model, but also receives undesirable flow characteristics of the tunnel due to the new location. Every unique position in a wind tunnel will present unique error data which must be mathematically eliminated from the end product data. This is due, e.g., to structural irregularities, shock wave reflection, and air velocity fluctuations. Because the probe must be moved over and over between readings to develop the bulk data set, the elimination of error data must be dealt with repeatedly. This makes the process very time intensive and difficult to perform. Further, extraneous character is incorporated into the data that does not represent the model.
It is desirable to measure off-body pressure signatures at several Mach numbers to thoroughly assess the aircraft design. The angles at which pressure waves emanate from the model are dependent on Mach number (i.e., the Mach angle). Therefore, collecting off-body pressure measurements at varying Mach numbers while maintaining a constant model height above the probe necessitates that the relative traverse position of the model and probe be varied. This may entail the unfavorable requirement of physically changing the fixed location of the probe in an effort to measure the extent of the pressure signature of interest. Not only will this cause undesirable variability in the data as stated above, it requires additional time and effort, reducing the efficiency and productivity of the testing procedure.
Similar to the above limitation, relocation of the fixed probe may be necessary if the Mach number is held constant but the model height above the probe is altered. In this scenario, the pressure wave sweep angles do not change, but because the model height above the probe changes, the pressure signature traverse position at the probe height changes. The probe must be repositioned in order to measure the extent of pressure signature. It is the conventional practice to collect pressure measurements at an array of conditions that include variations in both Mach number and model height.
Therefore, there is a need in the art for a system and method which enables the development of detailed signature data without the disadvantages noted above.